1. Field of the Invention
The present invention relates to a ceramic dielectric composition for temperature for compensation.
2. Description of the Prior Art
Japanese Patent Publication No. 17771/1981 of the Japanese patent application filed in the name of TDK Electronics Company Inc., Tokyo, Japan, discloses a composition of SrTiO.sub.3 --CaTiO.sub.3 --Nb.sub.2 O.sub.5 system by way of an example of a ceramic dielectric composition for temperature compensation exhibiting electrical characteristics of a dielectric constant of larger than 200, the temperature coefficient of a dielectric constant of up to -1000.times.10.sup.-6 /.degree.C. and quality factor (Q) of larger than 1000.
It has already been reported that such system exhibits electrical characteristics of the dielectric constant being 200 to 320 and of the quality factor being in the range of 1500 to 5000, in the range of the temperature coefficient of a dielectric constant of -1000.times.10.sup.-6 /.degree.C. to -3000.times.10.sup.-6 /.degree.C.
In addition, it has been confirmed that such system exhibits characteristics in which the dielectric constant is decreased in the ranges of 50 to 80% by weight of SrTiO.sub.3 and of 20 to 50% by weight of CaTiO.sub.3 in terms of proportion of SrTiO.sub.3 --CaTiO.sub.3 which is a principal constituent of the system, while the quality factor is increased as the temperature coefficient of a dielectric constant is decreased.
Generally, the electric characteristic of a ceramic capacitor is shown by the values by measurement of a sample of a ceramic element having electrodes of fired silver. The above described system is not an exception to the same and measurement has been made upon formation of electrodes of fired silver.
However, in view of the fact that the recent rise of the cost of silver per se has increased the cost of capacitors, ceramic capacitors using a base metal, such as nickel, copper or the like, cheaper than silver have been put into practical use. Usually, electrodes of a base metal are formed by an electroless plating method.
Accordingly, formation of electrodes by an electroless plating method on a ceramic element of the above described SrTiO.sub.3 --CaTiO.sub.3 --Nb.sub.2 O.sub.5 system can be readily considered. However, formation of electrodes of nickel or copper by an electroless plating method on a ceramic capacitor element made of such system has revealed a large difference, as compared with a sample having electrodes of fired silver. More specifically, although the quality factor has been in the range of 1500 to 5000 according to a sample having silver electrodes, the quality factor of a sample having nickel or copper electrodes remains as low as 200 at the most, revealing that an element which has electrodes formed by an electroless plating method can be hardly put into practical use. Therefore, in formation of electrodes a combination of a ceramic element with electrodes need be taken into consideration and, failure in formation of inexpensive electrodes by an electroless plating method is incompatible with cost reduction.
In the light of the foregoing, even when a ceramic element for capacitors having excellent electric characteristics can be obtained, it is undesirable that the ceramic element brings about degradation of electric characteristics in the case of electrodes of electroless plating. Therefore, it is desired that a ceramic element brings about no degradation of electric characteristics irrespective of whether electrodes are of fired silver or of an electroless plating method.